2.0 Analysis 2.1 Introduction The analysis will look at the decisions and action of the crew when the wheel failed during taxi, and the subsequent low power indication on take-off. 2.2 Wheel Failure There was no indication that the No. 2 wheel was damaged during the sharp radius turn at the terminal. There was no evidence found that differential braking or asymmetric power was used to augment the turn. The NDT inspection method last used on the No. 2 wheel by the previous American owner was an eddy current inspection after the fifth tire change, although the wheel manufacturer recommends an eddy current inspection after every tire change. The FDR data gathered on Russian operations indicates that the operations on the rough runways may impart an increase in wheel stress which may require increased inspection. 2.3 Crew Reactions to the Sounds of Tires Failing The bangs made while the aircraft was taxiing were heard by all of the crew on the flight deck, passengers, flight attendants, maintenance personnel at the company ramp area, and the loadmaster sitting in the cabin. The loadmaster was the only person who believed that the bangs were made by exploding tires. The aircraft, which was loaded to its maximum gross weight, had just taxied over the intersection of runway 07/25. The flight crew had discussed the sound and concluded that they were hearing an oleo bottom out. The flight crew had experienced rough runways in Russia, and may have been conditioned to the sound of banging oleos. The two inboard engines had been placed in idle reverse to avoid brake use on the slight decline, which resulted in higher noise levels on the flight deck. The cockpit crew, none of whom had experienced a tire failure on taxi before, were also wearing headsets which would attenuate external sounds. The bang would be louder for the occupants of the passenger cabin than for the flight crew since the main gear is located under the wing outboard of the cabin, 80 feet aft of the cockpit. The cockpit was also isolated from the passenger cabin by the bulkheads of the forward cargo hold, and the five pallets of crated cargo which probably muffled the sound. When the purser called the flight deck, she asked what the noise was, rather than describing what she and the flight attendant heard and felt. The response from the FE, which was given in a humorous manner, was interpreted to mean that everything was under control. This interchange between these two crew members was not effective in communicating the serious nature of what was heard. The physical limitations of the service interphone system in the aircraft allow only the purser to speak to the FE. If the captain or FO had been able to hear the call from the purser, they might have been cued to think about tires instead of oleos. The loadmaster, who had experienced a tire failure before, was reluctant to call a flight attendant or alert the flight crew before take-off, when he heard the tires fail. When the loadmaster finally went to the flight deck, after take-off, and told the flight crew of his suspicions, they were already aware of the rubber on the runway and paid little attention to his comments. As the captain stopped on the button of runway 34 in preparation for take-off, he was not aware that tires had failed. Although there was communication between some crew members and some persons were concerned, these concerns were not communicated to the captain. Had the concerns been brought to the captain's attention and analyzed collectively, it is possible that he would have responded differently. As it happened, each individual's concern was either intercepted or dismissed on its own. With a mind-set to go, it often takes strong evidence or a significant defect, readily apparent and unambiguous, to evoke a correct response. It is natural and human to seek to mitigate or rationalize against those stimuli which do not support the planned course of action. 2.4 Take-off When the power levers were advanced, the FE noticed that the No. 1 engine EPR was slow to increase. He had experienced exactly the same problem on the previous flight, and he advised the captain of the low EPR condition. Because of the low No. 1 EPR, the normal take-off challenge and response sequence was interrupted. When the N1 decayed from 103 per cent to 98 per cent, the FE expected the captain to reject the take-off, but the captain elected to continue, indicating he would fly N2. The sudden drop in No. 1 engine EPR recorded on the FDR at 111 knots ground speed likely corresponds to the N1 decay and enters the threshold of the high energy regime. The captain later indicated that there was no unusual yaw or sensation of power loss which would indicate low power, and that he therefore decided to continue the take-off. One strong cue available to the captain was the one and one-half knob throttle stagger that he would have felt when he placed his hand on the power levers. The manufacturer's AOL addresses rejected take-offs by stating, ...at speeds over V1 minus 20 knots, the captain may want to limit his reject option to engine failure only. The aircraft vibrated as it accelerated, and the flight crew were of the opinion that it was nose wheel shimmy; in reality, the vibration was caused by the two flat and disintegrating tires. The vibration was more pronounced in the cabin, but the purser did not consider it adverse enough to call the flight deck since she had not experienced a tire failure before. 2.5 Preparation for Emergency Landing Due to static interference in the interphone system when airborne, the purser had to walk up to the flight deck to receive instructions directly from the captain. The purser was advised twice that there would be an emergency landing and that there might be a fire on touchdown. The captain was of the opinion that the purser would carry out the required emergency procedures as outlined in her manual, and was not aware that this did not happen. The cabin crew's decision to not use the emergency checklist appears to have been made predominantly on the assumption that everything was going well to this point, and they did not want to alarm the passengers. The FE advised the purser on approach that the landing would be normal, when in reality an emergency landing was under way with potential for the worst possible outcome. 2.6 Maintenance The maintenance conducted on the No. 1 engine by the maintenance contractor prior to the occurrence was not effective in eliminating an intermittent low EPR discrepancy. 3.0 Conclusions 3.1 Findings The flight crew were certified and qualified for the flight in accordance with existing regulations. The aircraft was certified in accordance with existing regulations and approved procedures. The aircraft weight and C of G were within prescribed limits. The No. 2 wheel rim failed while the aircraft was taxiing as a result of an undetected fatigue crack, allowing the tire to deflate explosively. The No. 5 tire was punctured by a broken section of the No. 2 wheel rim. The flight crew, none of whom had experienced a tire failure while taxiing, mistook the bangs for a bottoming oleo. Communications between the purser and the flight deck were ineffective due to the design of the interphone system. The purser's call to the FE on the interphone to inquire about the bang was not effective in providing the flight crew with information about what was heard and felt in the cabin. The FE's humorous response to the purser's inquiry was interpreted to mean that everything was under control. The loadmaster, who was sitting in the cabin and who had previously experienced tire failures, did not advise the crew of his concerns until after the aircraft was airborne. The vibrations from the flailing main wheel tires were felt on the flight deck during take- off, but were misidentified as nose wheel shimmy. The vibration was more pronounced in the cabin, but the purser did not consider it adverse enough to call the flight deck during the take-off roll. On the take-off roll, the FE twice advised the captain that the No. 1 engine power indication was low. The captain elected to continue the take-off, while aware of a low No. 1 engine EPR, low N1, and a pronounced power lever stagger. The purser did not ensure that the flight attendants used the emergency checklists or briefed the passengers on the brace position, despite being advised by the captain to prepare for an emergency landing that might result in fire during touchdown. On approach, the FE advised the purser that the landing would be normal. At the time of the occurrence, the operator had never received maintenance or operations audits by TC. The flight crew may have become conditioned to bottoming oleos while operating on rough runways in Russia. The maintenance carried out on the No. 1 engine following the previous flight was not effective in eliminating the intermittent low EPR condition. The flight crew and cabin crew are trained separately in emergency procedures. The operator does not provide CRM training to its operational personnel, nor is it required by regulations. 3.2 Causes The No. 2 tire deflated while the aircraft was taxiing as a result of a wheel rim separation caused by an undetected fatigue crack. The No. 5 tire was punctured by a broken section of the No. 2 wheel rim. As a result of ineffective communications, the crew continued the take-off in an aircraft with two failed tires on the left side. Contributing to the ineffective crew communications was the lack of crew resource management training provided by the operator. 4.0 Safety Action 4.1 Action Taken 4.1.1 Operator Actions Following the occurrence, the operator's maintenance facility revised the pre-flight inspection form so that tire pressure leakage can be monitored. Safety memoranda concerning effective crew communication were also issued to flight crew. To increase the awareness of N1 and the procedure to reject the take-off at 80 knots in the event of low N1, the operator is now recording minimum N1 on their take-off data card for all take-offs. In addition, the operator indicated that other actions would be taken to enhance safety, including use of eddy current methods to inspect wheels at time of tire changes, measures to reduce strain on landing gear, establishment of a communications base station, modification of the aircraft interphone, appointment of a pilot to the company safety committee, joint cockpit/cabin crew emergency training, and re-allocation of duties which had been assigned to the VP Operations. 4.1.2 Transport Canada After the incident, Transport Canada (TC) carried out a cabin safety base inspection and coordinated in-flight inspections. This was followed by a base inspection which included flight operations and cabin safety and then an operations audit. TC requested and received amendments to the air carrier's operating manual, flight attendant manual, and crew training programs. The draft Canadian Aviation Regulations (CARs) will contain provisions to require air carriers to implement crew resource management (CRM) training and to conduct joint crew training with pilots and flight attendants. 4.1.3 Audits At the time of the occurrence, the operator had never received maintenance or operations audits by TC. The Manual of Regulatory Audits (MRA) calls for all companies to be audited six months after initial certification. In conjunction with information gathered from other occurrences over the past 10 years, the TSB identified shortcomings in the regulatory audit process of air carriers. In particular, it was found that TC audits lacked scope and depth, and that TC's verification of corrective action following the audits was inadequate. Therefore, the Board has recommended that: The Department of Transport amend the Manual of Regulatory Audits to provide for more in-depth audits of those air carriers demonstrating an adverse trend in its risk management indicators; The Department of Transport ensure that its inspectors involved in the audit process are able to apply risk management methods in identifying carriers warranting increased audit attention; The Department of Transport develop, as a priority, a system to track audit follow-up actions; The Department of Transport implement both short and long term actions to place greater emphasis on verification of required audit follow-up action and on enforcement action in cases of non-compliance. In response to these recommendations, TC has indicated that both recommendations A94-23 and A94-24 will be taken into consideration during amendments to the MRA. Also, TC will ensure that the Audit Procedures training program for inspectors takes into account recommendation A94-24 so that risk management methods are clearly understood and applied. With respect to recommendations A94-25 and A94-26, TC replied that the MRA will be reviewed to ensure clear policy direction is given to ensure effective audit follow-up systems are in place. Furthermore, an enhanced National Aviation Company Information System (NACIS) should be operational by September 1995 to track audit follow-up on a national basis. In the interim, a policy directive will be issued to regions to require a review of respective regional follow-up systems. 4.1.4 Crew Resource Management Ineffective crew communications contributed to this occurrence. Improving crew communication skills is an integral part of CRM training. Although CRM is currently not mandatory, Transport Canada's Standards of Training (to be enabled by the Canadian Aviation Regulations) includes a requirement that airline operators provide flight crew members with joint on-going CRM training. As a result of numerous occurrences in which inappropriate CRM and pilot decision making (PDM) were identified as contributing factors, the Board recently recommended that: The Department of Transport establish guidelines for crew resource management (CRM) and decision-making training for all operators and aircrew involved in commercial aviation; and The Department of Transport establish procedures for evaluating crew resource management (CRM) and pilot decision-making (PDM) skills on a recurrent basis for all aircrew involved in commercial aviation. In response to recommendation A95-11, TC has indicated that CRM and PDM training will be mandated for all air operators who are required to adhere to the Airline Operations regulations. In response to recommendation A95-12, TC has indicated that evaluation of CRM skills will be accomplished by way of a debriefing session following joint pilot/cabin crew recurrent training. Transport Canada is currently developing three human factors handbooks. The handbooks will include tools to evaluate attitudes, knowledge and skills for PDM, and will also include CRM measurement tools.